Conventional axle-hub assemblies include a stationary axle or spindle that supports a pair of spaced apart wheel bearings which, in turn, support a rotatable hub or wheel bearing housing. Most hub assemblies are constructed such that there is usually a lubricating cavity filled completely or partially with a lubricant, usually grease, that is applied to the bearings. Trailers such as boat trailers, utility trailers, cattle trailers, and the like, all utilize such wheel bearings assemblies.
Many present hub assemblies allow contaminants, e.g., dirty air and water, to enter the bearing housing contaminating the grease and reducing the effectiveness of and shortening the life of the hub assembly. The entry of such contaminants is generally related to variations of temperature and pressure in the bearing housing. When the housing is exposed to high temperatures, e.g., when the temperature increases as a trailer is being towed, gases, such as air, and grease, in the hub expand and are expelled from the structure. If the bearing assembly is packed tight with grease and designed so that no air or grease can escape without accommodating the pressure changes, the increased pressure in the hub causes damage to the bearing seals and the inside of the hub, which may not be immediately noticed but will result in the bearings becoming dry and freezing. When a hot trailer is suddenly cooled, e.g., when a boat trailer is submerged in water during boat launching, there is contraction of the grease and gases that tends to create a vacuum and suck water into the bearing housing. The water washes the grease from within the housing, causing the wheel bearings to be improperly lubricated and often ruined, due to friction and excessive heat while the trailer is towed.
The circumstances of use necessitate that the bearings be frequently lubricated, a time-consuming task. The trailer must be jacked up to free the wheel, the wheel and bearing hub removed, and the bearings then removed from the bearing housing in the wheel, washed free of old grease, repacked with new grease, and replaced in the bearing housing. Ultimately, one or both of the bearings will require replacement.
Various devices for lubricating wheel bearings and other bearings are known in the art. For example, some patents have addressed the problem of automatically supplying lubricant to a machine. See, for example, U.S. Pat. No. 915,731 issued to Brigham that discloses an oil chamber having multiple outlets from which oil is supplied to different parts of a machine to be lubricated, along with means for supplying the chamber with oil under pressure and control devices for regulating the automatic flow of oil through the outlets in a selected time period, and U.S. Pat. No. 2,526,568 issued to Leonard that discloses a lubricating apparatus which includes a measuring valve adaptable for use in a machine with either grease or oil as the lubricant.
Other patents have described systems for ascertaining the level of lubricant in a housing so that lubricant can be timely replaced. See, for example, U.S. Pat. No. 3,983,958 issued to Swearingen that discloses an apparatus designed for attachment to a bearing housing. The apparatus has an access conduit that allows observation of the level of the oil in the lubricating housing, thereby permitting a desired oil level in the bearing housing to be maintained. U.S. Pat. No. 960,341 to Kincaid discloses a grease reservoir adapted to contain a stick of semi-solid lubricant. The reservoir serves as an auxiliary grease chamber and includes a spring-press plunger adapted to indicate the quantity of grease contained in the reservoir.
Other devices, many of which are patterned after the aforementioned Kincaid patent, are self-lubricating devices. These devices include a grease chamber disposed within a cylindrical housing, a spring-loaded plate slidably mounted in the housing, a grease fitting provided in the housing for charging the housing with grease and forcing the spring-loaded plate outwardly. The spring-loaded plate continually exerts pressure against the grease and causes the grease to enter the wheel bearing housing and coat the wheel bearings. Patents that describe such a spring-loaded piston system include U.S. Pat. No. 4,941,550 issued to Blake, U.S. Pat. No. 4,784,500 issued to Prokop, U.S. Pat. No. 4,106,816 issued to August, and U.S. Pat. Nos. 4,190,133 and 4,058,185 issued to Ploeger.
Still other prior art devices have addressed the problem of pressure changes in the wheel hub especially in particular applications where the bearing houses are exposed to high temperatures. Such devices incorporate a flexible diaphragm in the device. See, for example, U.S. Pat. No. 2,676,073 issued to Boden (railway cars) and U.S. Pat. No. 4,039,229 issued to Ohlberg (grate cars for sintering machines).
The self-lubricating devices, however, tend to be very complex structures. Most lack facility for quickly determining when the housing needs recharging with grease and do not permit quick and efficient recharging, without overcharging. Moreover, for those devices that attempt to use diaphragms to accommodate pressure changes, the construction typically requires isolation of the diaphragm from the grease lubricant.
Despite recognition of the many practical problems associated with lubrication of wheel hubs, proper solution to all these problems in a single device has not yet been demonstrated in the prior art. None of the prior art devices provides a lubricating device of simple construction that is sealed and eliminates water and other contaminants from being drawn into the hub, adjusts to temperature and pressure differentials in the hub, and utilizes an easy to handle, fluid lubricant which facilitates charging of the hub.